15 IN VIVO PROGESTERONE RELEASE KINETICS: A COMPARATIVE STUDY OF DIFFERENT INTRAVAGINAL DEVICES USED IN CATTLE

Abstract

Intravaginal progesterone (P4) releasing devices are widely used in hormonal protocols for fixed-time artificial insemination (FTAI). To reduce production cost in Brazilian farms, after first use these devices are currently reused once or twice, providing good reproductive efficiency in cattle. The aim of this study was to compare P4 plasma concentrations among time in ovariectomized cows receiving 3 different commercially available devices: Sincrogest^® (SIN, 1 g of P4), Cronipres^® (CRO, 1 g of P4 and 3 rings of 0,1 g of P4 for the third use) and Primer^® (PRI, 1 g of P4). For each type, new (1st use, n = 2), once-used (2nd use, n = 2) and twice-used (3rd use, n = 2) devices were tested. Blood samples were collected at times 0 (before device insertion), 2, 4, 8, 10, 12, 24, 48, 72, 96, 120, 144, 168, and 192 h (Day 0 to Day 8). P4 plasma concentrations were measured by radioimmunoassay and the averages for each experimental group were submitted to analysis of variance adding repeated-measures in time factor. Comparisons were made among 3 types of device in each of 3 uses. P4 concentrations (ng mL^–1) and standard deviation in the periods in which there was statistical difference (P < 0.05; ^a,b,cdifferent letters in the same period differ statistically) were as follows: First use: the 3 brands did not differ during the test and in Day 8 P4 levels remained near 2 ng mL^–1. Second use: 2 h – SIN (3.7 ± 0.8)^ab, CRO (5.4 ± 0.4)^a, PRI (3 ± 0.4)^b; 6 h – SIN (4 ± 0.5)^a, CRO (4.9 ± 0.2)^a, PRI (2.9 ± 0.3)^b; and 144 h – SIN (2.2 ± 0.4)^b, CRO (0.8 ± 0.3)^a, PRI (1.3 ± 0.1)^ab. On Day 8, Primer^® and Sincrogest^® P4 levels remained between 1 and 2 ng mL^–1, whereas Cronipres^® levels remained below 1 ng mL^–1. Third use: 2 h – SIN (3.2 ± 0.04)^b, CRO (7.9 ± 0.5)^a, PRI (2.4 ± 0.2)^b; 4 h – SIN (2.4 ± 0.4)^b, CRO (5.4 ± 0.2)^a, PRI (2.8 ± 0.3)^b; 6 h – SIN (2.5 ± 0.8)^b, CRO (7.4 ± 1.8)^a, PRI (2.7 ± 0.5)^b; 8 h – SIN (2.3 ± 0.2)^b, CRO (5.3 ± 1.4)^a, PRI (2 ± 0.1)^b; 10 h – SIN (3.1 ± 0.2)^b, CRO (5.5 ± 0.5)^a, PRI (2.5 ± 0.2)^b. 12 h – (2.7 ± 1.3)^b, CRO (5.8 ± 0.6)^a, PRI (2.2 ± 0,1)^b; and 120 h – SIN (1.3 ± 0.2)^a, CRO (0.9 ± 0.2)^b, PRI (0.8 ± 0.04)^b. On Day 8, all levels remained below 1 ng mL^–1. In this study, P4 released concentrations differed in 3 of 15 periods in second-use device tests. In third-use device tests, Cronipres^® released significantly more P4 from 2 to 12 h. It is unclear, however, if greater release of P4 in the first 24 h is advantageous, considering that Sincrogest and Primer^® P4 concentrations remained above 2 ng mL^–1. Additionally, it was noticed that P4 release decreased according to the number of previous uses. These findings suggest a variety of possibilities matching different device brands and different animal categories depending on animal steroid metabolism rate and consequent need for exogenous P4 supplementation. However, for such a claim, further studies on this topic are needed.